U.S. patent number 4,749,330 [Application Number 06/863,084] was granted by the patent office on 1988-06-07 for transport mechanism.
Invention is credited to Derek L. Hine.
United States Patent |
4,749,330 |
Hine |
June 7, 1988 |
Transport mechanism
Abstract
A transport mechanism for silicon wafers comprises an elongate
four arm linkage and a wafer support arm which is secured to the
linkage through a gearing system. One of the short arms of the
linkage is fixed, and as the linkage is rotated, the gearing system
produces a different motion in the support arm. Preferably pinion
gears are secured to the ends of the long arms and engage a pinion
gear secured to one end of the support arm, so as to produce linear
motion of a wafer placed on the support arm.
Inventors: |
Hine; Derek L. (Portola Valley,
CA) |
Family
ID: |
25340199 |
Appl.
No.: |
06/863,084 |
Filed: |
May 14, 1986 |
Current U.S.
Class: |
414/744.5;
414/917; 414/935; 74/103; 74/469; 74/98; 901/25 |
Current CPC
Class: |
B25J
9/1065 (20130101); Y10S 414/13 (20130101); Y10T
74/18928 (20150115); Y10T 74/20 (20150115); Y10T
74/1888 (20150115); Y10S 414/135 (20130101) |
Current International
Class: |
B25J
9/10 (20060101); B25T 009/06 () |
Field of
Search: |
;414/744B,744A,752,733,917 ;901/25 ;74/98,103,469
;33/25.1,25.3,441 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Spar; Robert J.
Assistant Examiner: Underwood; Donald W.
Claims
I claim:
1. Apparatus for transporting a silicon wafer along a linear path
from a first position to a second position, which apparatus
comprises:
(1) a base,
(2) a four arm linkage comprising
(a) a first arm which is fixed relative to the base and which has a
first end and a second end,
(b) a second arm which is substantially longer than the first arm
and which has a near end and a far end, the near end being
rotatably secured to the first end of the first arm;
(c) a third arm which is of the same length as the second arm and
which has a near end and a far end, the near end being rotatably
secured to the second end of the first arm; and
(d) a fourth arm which is of the same length as the first arm and
which has a first end rotatably secured to the far end of the
second arm and a second end rotatably secured to the far end of the
first arm;
(3) a first pinion gear which is secured to the second arm at the
far end thereof;
(4) a wafer support arm which has a pivot end and a wafer support
end, the wafer support end being adapted to carry a silicon
wafer;
(5) a second pinion gear which is secured to the wafer support arm
at the pivot end thereofand which is maintained in enagement with
the first pinion gear as the second arm is rotated relative to the
first arm; and
(6) a third pinion gear which is secured to the third arm at the
far end thereof and which is also maintained in engagement with the
second pinion gear as the second arm is rotated relative to the
first arm;
whereby, when a wafer is placed on the wafer support arm and the
second arm is rotated relative to the first arm, the wafer is
transported along a linear path.
2. Apparatus according to claim 1 wherein the second, third, fourth
and wafer support arms rotate in different planes about pivots
which do not extend into adjacent planes of rotation, whereby the
four arm linkage can be rotated through two extreme positions in
each of which all the pivot points between the arms are in a
straight line.
3. Apparatus according to claim 1 which comprises means for
rotating the second arm.
4. Apparatus according to claim 1 wherein the wafer support arm is
an auxiliary four arm linkage comprising
(a) an auxiliary first arm which has a first arm which has first
end and a second end, and which is in a fixed position relative to
the second arm,
(b) an auxiliary second arm which has a near end and a far end, the
near end being rotatably secured to the first end of the auxiliary
first arm,
(c) an auxiliary third arm which is of the same length as the
auxiliary second arm, and which has a near end and a far end, the
near end being rotatably secured to the second end of the auxiliary
first arm, and
(d) an auxiliary fourth arm which is of the same length as the
auxiliary first arm and which has a first end rotatably secured to
the far end of the second arm and a second end rotatably secured to
the wafer support end of the wafer support arm,
whereby when a wafer is placed on the wafer support arm and the
second arm is rotated relative to the first arm, the wafer is
transported along a linear path without rotational motion.
5. A method of transporting a silicon wafer, which method comprises
placing the wafer on the wafer support section of an apparatus as
defined in claim 1 and rotating the four arm linkage.
6. Apparatus according to claim 1 wherein the second pinion gear is
mounted within a bracket, and the bracket is secured to the fourth
arm so that the second pinion gear is spring-loaded into engagement
with the first and third pinion gears.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to apparatus for transporting silicon wafers
or the like, and methods of using such apparatus.
2. Introduction to the Invention
In the manufacture of solid state electronics devices, silicon
wafers are moved between different work stations, generally in
cassettes which hold a number of wafers stacked one above the other
in horizontal pockets, each pocket being in the form of a generally
U-shaped horizontal groove into which a wafer can be placed.
Careful handling of the wafers is essential; in particular
insertion and extraction of wafers into and from cassettes require
a linear motion in order to minimize damage to the wafers and the
production of particulate contaminants. In many cases, it is
desirable that the wafer should have a known orientation at the
work station, and hence also a known orientation in the
cassette.
Currently used transport mechanisms for silicon wafers include belt
transports and air tracks, but these mechanisms have been
criticized as likely sources of particles which can contaminate the
wafers. U.S. Pat. Nos. 4,433,951 and 4,483,654 (Koch and Peterson,
assigned to Lam Research Corporation), the disclosures of which are
incorporated herein by reference, describe a transport mechanism in
which the rotational motion of a support arm is transmitted through
a series of gears to a workpiece arm shaft having one end rotatably
secured to the support arm, so that rotation of the support arm
effects linear motion (or other predetermined motion) of a
workpiece placed at the other end of the workpiece arm shaft.
SUMMARY OF THE INVENTION
I have discovered an improved transport mechanism which makes use
of a combination of (a) a multi-arm linkage which can be caused to
rotate about a fixed base and (b) a support arm which is secured to
the linkage through (c) a gearing system, so that, when the linkage
is rotated, the rotational movement of the linkage results in a
related but different rotational movement of the support arm. In
this way, a silicon wafer (or other load) placed on the support arm
can be transported along a predetermined non-circular, preferably
linear, path which depends upon the lengths of the arms and the
gearing system.
The linkage preferably comprises two long arms each having a first
length, and two short arms which join the ends of the long arms and
each of which has a second length which is less than the first
length, eg. from 0.1 to 0.5 times the first length; the four arms
are rotatably secured to each other, and one of the short arms is
fixed relative to a base. When the three rotatable arms are rotated
(for example by means of a motorized driving shaft coaxial with the
pivot point between one of the long arms and the fixed short arm),
the area enclosed by the arms (typically a parallelogram) changes.
If the second, third, fourth and support arms rotate in different
(but parallel) planes about pivots which do not extend into
adjacent planes of rotation, the four arm linkage can be rotated
through two extreme positions in each of which all the pivot points
between the arms are in a straight line. The arms of the linkage
can be straight, but need not be, and the term "arm" is used herein
in a broad sense to include any physical structure which will
permit the desired operation of the apparatus. For example, the
fixed arm can be provided by two pillars which are mounted on the
base to provide fixed pivot points for the long arms, in which case
the base and the pillars together provide the short fixed arm.
The gearing system which connects the linkage and the support arm
can be very simple, and preferably comprises (a) a first pinion
gear which is secured to one of the rotatable arms and (b) a second
pinion gear which is secured to the support arm and which is
maintained in engagement with the first pinion gear as the
rotatable arms of the linkage are rotated. The first pinion gear is
preferably secured to one of the long arms at the end thereof
remote from the fixed short arm. The second pinion gear is
preferably secured to the support arm at one end thereof. The first
and second pinion gears are preferably of the same size, so that
rotation of the second arm results in an equal rotation of the
support arm but in the opposite direction. This will result in
linear motion of that section of the support arm (and/or of a wafer
placed on the support arm) whose distance from the pivot point of
the support arm is equal to the distance between the pivot points
of each of the long arms. The linear motion passes through a point
which is close to the pivot point between the first arm and the
long arm carrying the pinion gear, but offset from that pivot point
by a distance equal to the gear offset.
When the linkage is rotated through a position in which all the
pivot points between the arms are in a straight line, or close to
such a position, the linkage tends to become unstable and
positioning of the support arm tends to become less accurate. In a
preferred embodiment of the invention, this tendency is controlled
by using a gearing system in which a gear on the support arm is
driven by gears on at least two of the rotatable arms of the
linkage. Preferably first and third pinion gears (which must be of
the same size) are secured to the long arms at the respective ends
thereof remote from the fixed short arm, and a second pinion gear
is secured to the support arm and is maintained in engagement with
the first and third pinion gears as the linkage is rotated.
Preferably the second pinion gear is of the same size as the first
and third pinion gears, so that linear motion of the support arm is
obtained.
If desired, a similar gearing system, but without a support arm,
can be used to stabilize the linkage at the fixed arm.
With a simple support arm, the transport of a wafer (or like
object) along a defined, preferably linear, path will be
accompanied by a defined degree of rotation. In some cases this is
not a problem; in other cases, it is valuable if the wafer can be
delivered in a different orientation (or close to it), so that the
step of orienting the wafer at the work station is eliminated or
made quicker and cheaper. This desirable result can be achieved by
using a wafer support arm which is an auxiliary four arm linkage
comprising one arm which is in a fixed position relative to the
travelling short arm of the main linkage. If the auxiliary four arm
linkage is identical to the main linkage, rotation of the wafer can
be eliminated entirely. If the auxiliary linkage is different, then
there will be a predictable degree of rotation which is less than
that with a simple support arm.
The support arm can if desired comprise two or more auxiliary
linkages successively connected through each other to the main
linkage in the same way as is described above, in order to provide
linear (or other predictable) motion over longer distances.
However, care must be taken to ensure that the arm is sufficiently
strong and rigid.
The gear on the support arm must be maintained in engagement with
the gear or gears on the linkage. This is preferably achieved by
spring loading the gears into each other or by using other known
anti-backlash methods, which helps to make the apparatus more
stable and to eliminate or reduce backlash.
BRIEF DESCRIPTION OF THE DRAWING
The invention is illustrated in the accompanying drawing, in
which
FIG. 1 is a plan view of apparatus of the invention,
FIG. 2 is a side view of the apparatus of FIG. 1,
FIG. 3 is a perspective view, partly cut away, of part of the
apparatus of FIG. 1, and
FIG. 4 is a diagrammatic view of another apparatus of the invention
in which the support arm comprises an auxiliary four arm
linkage.
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of the invention is an apparatus which
comprises
(1) a base,
(2) a four arm linkage comprising
(a) a first arm which is fixed relative to the base and which has a
first end and a second end,
(b) a second arm which is substantially longer than the first arm
and which has a near end and a far end, the near end being
rotatably secured to the first end of the first arm;
(c) a third arm which is of the same length as the second arm and
which has a near end and a far end, the near end being rotatably
secured to the second end of the first arm, and
(d) a fourth arm which is of the same length as the first arm and
which has a first end rotatably secured to the far end of the
second arm and a second end rotatably secured to the far end of the
first arm;
(3) a first pinion gear which is secured to the second arm at the
far end thereof;
(4) a wafer support arm which has a pivot end and a wafer support
section, the wafer support section being adapted to carry a silicon
wafer;
(5) a second pinion gear which is secured to the wafer support arm
at the pivot end thereof and which is maintained in engagement with
the first pinion gear as the second arm is rotated relative to the
first arm;
whereby, when a wafer is placed on the wafer support arm and the
second arm is rotated relative to the first arm, the wafer is
transported along a linear path.
Referring now to FIGS. 1-3 of the drawing, these illustrate an
apparatus which comprises a base 1; a four arm linkage 2 which
comprises a first short arm 21 which is fixed to the base, a second
long arm 22, a third long arm 23, and a fourth short arm 24; and a
motor 8 for rotating the linkage about the base. The arms and the
pivots between them are arranged so that the arms rotate in
parallel but different planes. Secured to the end of arm 22 is
pinion gear 3, and secured to the end of arm 23 is identical pinion
gear 6. Wafer support arm 4 has a pivot end 41 and a wafer support
section 42 which can carry a silicon wafer 19 (shown in FIG. 2
only). Secured to the pivot end 41 is a pinion gear 5 which is
identical to pinion gears 3 and 6. The pinion gear 5 is rotatably
mounted within a bracket 7 and is spring-loaded into engagement
with pinion gears 3 and 6 by means of shoulder screws 71 and
Belleville springs 72 which secure the bracket 7 to the short arm
24. Alternative means for springloading the pinion gears into
engagement can of course be used.
Referring now to FIG. 4, this shows a four arm linkage 2 and a
support arm 4 as in FIGS. 1-3 with an auxiliary four arm linkage 9
between linkage 2 and support arm 42. The auxiliary linkage
comprises short arms 91 and 94 and long arms 92 and 93. Short arm
91 is maintained in a fixed position relative to short arm 24 by
means of identical pinion gears 97 and 98 which are maintained in
engagement with pinion gears 6 and 3. Arms 92 and 93 are secured to
identical pinion gears 93 and 96 which engage the pinion gear 5
secured to the support arm 4.
* * * * *